2440 vs. 2441

[Mr. Widget]

I was talking to a friend who has made custom Be diaphragms for JBL large format drivers... he told me that his Be diaphragms will work with 2440(375) motors but not 2441 motors as the gap depth, not width, is shorter and the new diaphragms will not fit properly. I have always been under the impression that the 2441 was a 2440 with a different diaphragm.

I know oldmics has a collection of older 375s, if anyone could verify the gap depth of the 375 or 2440 vs. the 376 or 2441 I'd really appreciate it.

Widget

[yggdrasil]

I have a 2441 I can measure tomorrow. I'll pass on removing the red wax seals on my 375's just now... (they work)

[scott fitlin]

I have a 2441 I can measure tomorrow. I'll pass on removing the red wax seals on my 375's just now... (they work)

I have two 2440 drivers sitting on a shelf, I will measure these as best I can. Then post info!

[speakerdave]

What is the width of the top plate on the 2440 and on the 2441?

Looks to be about 19/64 (I think that's about 8mm) on the 2441.

[scott fitlin]

Using a card in the gap, and marking it, then measuring it, I come up with 10/32 in. depth for the gap of a 2440 driver. I am not sure if my measurement is accurate, but seems to be fairly so. I am using a Brown and Sharpe set of calipers to measure with.

[Guido]

Widget does this mean you have access to Be Dias for 2440 Drivers?

Are they available for forum members?

Did you ever measure one with Clio?

[Earl K]

Hi Widget

I know oldmics has a collection of older 375s, if anyone could verify the gap depth of the 375 or 2440 vs. the 376 or 2441 I'd really appreciate it.

- I also happen to store some 2440s & 2441s here at home .
- I'll measure the top-plates tonight ( from the outside )
- I also believe I have a single 2441 ( with its' diaphragm removed ), making an actual in-gap measurement doable, tonight also .
- As implied already, an outside measurement ought to suffice here.

Anyways <>

PS - Oh , here are some shots from an eBay seller called "Audiobin" who demags / rebuilds / & remags these big guys ( he is unfortunately caught up in a dispute with the German buyer who purchased the set shown ) . Widget you might want to speak with this guy. He's stated some interesting things in his eBay sale copy .

[Mr. Widget]

He may be mistaken, but has been a reliable source of info in the past. Hopefully with this group on it we will come up with a definitive answer.

Widget does this mean you have access to Be Dias for 2440 Drivers?

Are they available for forum members?

Did you ever measure one with Clio?

I have not measured one, but did listen to a pair and was impressed. I am investigating the possibility of having a small batch run. I'll post the pricing and availability info when I get it.

Widget

[edgewound]

2440 and 2441 are physically identical, along with the 2445, 2446, 2447, 2450, 2451 all being mechanically identical...that's why the diaphragms are intechangeable. 2482, 2485's don't share these interchangeabilities, but Radian Audio does manufacture aluminum diaphragms for these beasts.

Hope that helps,

Edgewound

[Mr. Widget]

2440 and 2441 are physically identical, along with the 2445, 2446, 2447, 2450, 2451 all being mechanically identical...

That is what I have always been told... are you certain of the gap depth?

The published specs are different with the 2440 rated at 20,500 gauss and the 2441 at 18,000 gauss.

I have always assumed that this was due to different measurement techniques.

Widget

[scott fitlin]

That is what I have always been told... are you certain of the gap depth?

The published specs are different with the 2440 rated at 20,500 gauss and the 2441 at 18,000 gauss.

I have always assumed that this was due to different measurement techniques.

Widget

If the gap depth of 40 and 41 are the same, I am down to try some Be diaphragms for my JBL,s!

Lets do it once we got our answers!

[edgewound]

Gap depths have to be the same for diaphragm interchangeability. The gaps are deeper in the 2482 & 2485 that came with phenolic diaphragms. My 1976 JBL Professional with catalog with 2440 & 2482 says 20,500 gauss for all the large format drivers, my 1980 catalog says 18,000 gauss for both 2441 & 2482....both catalogs state 118dB sensitivity for these same drivers. I can't explain the difference in gauss....you're theory sounds good.


I haven't measured them,though...for the diaphragms to be truly, usefully interchangeable, the top plate gap depths must be the same for the voice coils to be symmetrical from either end of the gap...or they'd be terribly distorted.

Thanks,

Edgewound

[gibber]

Gap depths have to be the same for diaphragm interchangeability. The gaps are deeper in the 2482 & 2485 that came with phenolic diaphragms. My 1976 JBL Professional catalog with 2440 & 2482 says 20,500 gauss for all the large format drivers, my 1980 catalog says 18,000 gauss for both 2441 & 2482....both catalogs state 118dB sensitivity for these same drivers. I can't explain the difference in gauss....you're theory sounds good.

I haven't measured them,though...for the diaphragms to be truly, usefully interchangeable, the top plate gap depths must be the same for the voice coils to be symmetrical from either end of the gap...or they'd be terribly distorted.

Thanks,

Edgewound

Hope nobody minds if i post to a 10-yr old thread, i stumbled over this today and do know the following from the 2440, 2441 and 2482 cores that i have tried to measure. When re-magging, i noticed that the probe of my cheap HT-20 Teslameter (the black, not brown probe) would just fit into the gaps of 2441 & 2482, but not into the 2440 gap => the reason for the stated higher flux density is maybe gap width.

After re-magging at a friend's, we got the following (hope i remember it correctly) on his pro-quality meter
2440 : below 2T (around 19.800 Gauss, we did quite a few. Why not 2.05T => Widget mentioned a meas accuracy issue in early JBL specs)
2441 : exactly 1.8T (on four samples)
2482 : just below 1.7T (16.700 to 16.950 on 4 samples)

Assuming the gap width of 2482 and 2441 is the same, info in this thread that 2482 has slightly more (inside) pole plate thickness may account for the flux density difference to 2441. My Apr.'84 data sheet of 2482 states 1.7T, earlier specs 1.8T (see above).

As to the difference between 2441 and 2440, i have read elsewhere on this site that JBL was forced to do it because the higher power delivered by transistor amps would mean that heat would make coils expand more in the gap, giving rise to reliability issues with customers. Which JBL apparently reacted to by making the gap wider on 2441. The simultaneous fram change meant unchanged mid output.

I am sure most of this info is elsewhere on this site, hope someone finds it useful here. Btw, all these cores are sold, i'm into D502's currently. I believe TAD's reworked TD4003/2002 plug, Yamaha's JA6681 and JBL "Coherent" all borrowed from it.

Talking of which: who can borrow/sell me my 2nd 476Be to finally try that baby with Be fram, silver-on-pole and "coherent" plug in stereo ?

Enjoy the Sunday,
Ralph

[Earl K]

2441 - As best as I can measure ( cardboard in the gap / with a sharp line drawn across top ) ; the depth appears to me as 8 mm .

- Perhaps your contact is referring to a difference in the coil-winding depths between the two diaphragm types.

- Does he by-chance attach these new Be domes to an existing old coil/surround with its' bakelite ring ?


- did you look at the contact info mentioned within my last post ?